U.S. Pat. No. 4,616,198 entitled "Contact Arrangement for a Current Limiting Circuit Breaker" describes the early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let-through upon the occurrence of an overcurrent condition.
When the contact pairs are arranged upon one movable contact arm such as described within U.S. Pat. No. 4,910,485 entitled "Multiple Circuit Breaker with Double Break Rotary Contact", some means must be provided to insure that the opposing contact pairs exhibit the same contact pressure to reduce contact wear and erosion.
One arrangement for providing uniform contact wear is described within U.S. Pat. No. 4,649,247 entitled "Contact Assembly for Low-voltage Circuit Breakers with a Two-Ann Contact Lever". This arrangement includes an elongate slot formed perpendicular to the contact travel to provide uniform contact closure force on both pairs of contacts.
U.S. Pat. No. 5,030,804 entitled "Contact Arrangement for Electrical Switching Devices" describes providing a pair of cylindrical plates on either side of the contact arms and forming elongated slots within each of the cylindrical plates.
Other examples of circuit breakers employing rotary contacts are found in U.S. Pat. No. 5,281,776 entitled "Multipole Circuit Breaker with Single Pole Units; U.S. Pat. No. 5,310,971 entitled "Molded Case Circuit Breaker with Contact Bridge Slowed Down at the End of Repulsion Travel"; and U.S. Pat. No. 5,357,066 entitled "Operating Mechanism for a Four-Pole Circuit Breaker".
State of the art circuit breakers employing a rotary contact arrangement employ a rotor assembly and pair of powerful expansion springs to maintain contact between the rotor assembly and the rotary contact arm as well as to maintain good electrical connection between the contacts, per se. The added compression forces provided by the powerful expansion springs must be overcome when the contacts become separated by the contact "blow open" forces of magnetic repulsion that occur upon extreme overcurrent conditions within the protected circuit before the circuit breaker operating mechanism has time to respond.
One purpose of the invention is to describe a rotary contact arrangement having expansion springs arranged between the rotary assembly and the rotary contact arm that maintain good electrical connection between the contacts during quiescent operating current conditions while enhancing contact separation upon occurrence of extreme overcurrent conditions.